Thixotropic printing ink compositions and methods of preparing same
BACKGROUND OF THE INVENTION 
     The present invention relates generally to the chemical arts and more particularly to thixotropic oil and/or resin-based ink compositions and methods of preparing same. 
     Various printing ink compositions have heretofore included thixotropic chemical compounds and/or organophilic clay gelant materials for purposes of imparting desired thixotropic properties to the ink. However, many chemical compounds used as thixotropic agents of the prior art require the application of substantial heat in order to obtain the desired rheological properties. Additionally, clay-type thixotropic agents tend to swell as they absorb oil and, because clay thixotropic agents are generally prepared in powder form, they often require vigorous mixing in order to obtain a final smooth ink composition. Such clay-type thixotropic agents also greatly reduce the gloss of certain heatset inks. 
     Accordingly, there exists a need in the art for improved thixotropic agents for use in organic-based (e.g. oil-based, resin-based) ink systems. It is desirable that such improved thixotropic agents be easily misable or dissolvable in organic ink vehicles. Additionally, it is desirable that such improved thixotropic agents be usable at room temperature or at normal ink manufacturing/processing temperatures without the necessity of increasing such temperatures to gain effective thixotropic effects. Furthermore, any such thixotropic agents should not diminish or detract from any desirable physical, chemical, and visual properties of the ink compositions in which they are incorporated. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes some or all of the shortcomings of the prior art by identifying and providing new thixotropic agents for use in organic based (e.g. oil based and/or resin based) printing ink compositions. The new thixotropic agents of the present invention offer the advantage of being usable at room temperature and/or normal processing temperatures and also have been found to bring about desirable improvement in the rub resistance of certain printing inks. 
     In general, the printing ink compositions of the present invention comprise (a) at least one organic ink vehicle, (b) at least one ethanolamine compound, and (c) at least one color-imparting material, such as a pigment. The ethanolamine compound(s) is/are combined with the organic ink vehicle and pigment in sufficient concentration to provide a composition which exhibits desirable thixotropic properties as well as physical, chemical, and visual/color characteristics suited to the intended application. 
     The organic ink vehicles usable in ink compositions of the present invention include various (a) ink oils and (b) organic resins and/or combinations thereof. 
     Examples of ink oils which are preferably used in the present invention include naphthenic ink oils. One presently preferred naphthenic ink oil which is usable in the present invention is commercially available as Hyprint L-1200 (Ergon Refining, Vicksburg, Miss.) and has an average molecular weight of about 442 gm/mol. The carbon atom breakdown of this presently preferred naphthenic ink oil is as follows: 
     12% aromatic carbon atoms 
     40% naphthenic carbon atoms 
     48% paraffinic carbon atoms 
     Examples of organic resins which may be used in the present invention include various high and low molecular weight resins. Generally, it is desirable to employ a resin, or combination of resins, which will result in a final ink formulation exhibiting a maximum water takeup of 40%-60% by weight. In particular, it has been found that an acceptable organic resin vehicle may be formed by combining one high molecular weight hydrocarbon resin having an average molecular weight of approximately 20,000-35,000 gm/mol (HSLM Resin, Resinol Corp., Hattiesburg, Miss.), with one lower molecular weight resin, such as resin having an average molecular weight of approximately 950 gm/mol (1420 Resin, Nevile Chemical Co., Pittsburg, Pa.). The relative amounts of these two resins are then adjusted so as to provide a final ink having the desired 40%-60% hydroscopicity. 
     One of the preferred resin compositions for use in connection with the present invention is known to be prepared from (a) tall oil fractions, (b) unsaturated hydrocarbon resin, (c) dienophile modified polymer, and (d) pentaerythritol (HSLM Resin, Resinol Corp., Hattiesburg, Miss.). Other resin compositions are, of course, also usable in connection With this invention. 
     The ethanolamine thixotropic agents which may be used in the present invention include monoethanolamine, diethanolamine, and/or triethanolamine. Of these, triethanolamine is presently preferred for use as a thixotropic additive in oil and/or resin-based printing ink compositions. In addition to their ability to impart desirable rehological properties, the inclusion of ethanolamine compounds, such as TEA, within the ink compositions of the present invention has been found to bring about improved rub resistance of the applied printing ink. Such improvement in rub resistance is identified as an additional advantage to be gained by incorporating the ethanolamine compounds of the present invention into ink compositions used in applications wherein rub-off is a typical problem (e.g., newspaper printing applications). 
     The color-imparting additives employable in ink compositions of the present invention include various pigments and/or pigment-containing pastes. Pre-dispursed pigment pastes generally comprise one or more colored pigments dispursed in a vehicle and/or solvent. The vehicle(s) employed in such pre-dispursed pigment paste may comprise one or more of the organic ink vehicles described herein as basic components of ink compositions of the present invention and/or other vehicles which differ from the above-described organic ink vehicles. 
     The printing ink compositions of the present invention may be prepared at room temperature without the addition of extraneous heat. Such printing ink compositions are known to exhibit desirable thixotropy as Well as increased rub resistance. It is probable that these compositions will also exhibit other improved properties and advantages. Indeed, additional other objects and advantages of the invention may become apparent :o those skilled in the art upon reading and understanding of the various examples and data set forth herein. 
    
    
     EXAMPLES 
     The following examples are provided for purposes of describing and illustrating the present invention. These examples represent ink compositions (i.e. ingredients and relative amounts thereof) which may be prepared in accordance with the present inventive concept. These examples are not intended to limit the scope of the invention or the claims set forth herein. 
     EXAMPLE I 
     A black ink formulation in accordance with the invention comprises the folloWing formula: 
     
         ______________________________________                                    
BLACK INK FORMULATION                                                     
                                Approxi-                                  
                                mate                                      
                 Tradename/     % By                                      
Component        Source         Weight                                    
______________________________________                                    
Petroleum-Based Ink Solvent                                               
                 Magiesol 52 Oil;                                         
                                33.70%                                    
(hydro-treated 52A Oil)                                                   
                 Magie Brothers                                           
                 Oil Co., Franklyn                                        
                 Park, Illinois                                           
Modified Hydrocarbon Resin                                                
                 1420 Resin; Nevile                                       
                                10.50%                                    
(average molecular weight                                                 
                 Chemical Co.,                                            
about 950)       Pittsburgh, PA                                           
Modified Hydrocarbon Resin                                                
                 HSLM Resin;    8.50%                                     
(average molecular weight                                                 
                 Resinol Corp.                                            
20,000-35,000)   Hattiesburg, MS                                          
Petroleum-Process Oil                                                     
                 Telura 797; Exxon                                        
                                4.50%                                     
                 Chemical Corp.                                           
                 Houston, TX                                              
Oil-Based Carbon Black                                                    
                 ELFEX 115;     17.55%                                    
                 Cabot Corp.,                                             
                 Cabot, LA                                                
Aluminum Gellant Cyclogel;      .63%                                      
                 Chattem Chemical,                                        
                 Chattanooga, TN                                          
Naphthenic Ink Oil                                                        
                 Hyprint L-1200;                                          
                                24.55%                                    
(1-1200 Oil)     Ergon Refining,                                          
                 Vicksburg, Miss.                                         
Triethanolamine (TEA)                                                     
                 Union Carbide Corp.                                      
                                0.07%                                     
                 Princeton, NJ                                            
______________________________________                                    
 
    
     The above-set-forth formulation is prepared by blending all components in a single vessel. 
     The percentages set forth in the above example provide an ink formulation which is usable in many (lithographic) newspaper printing operations. However, it will be appreciated that adjustments in the viscosity range, tack and/or other properties of the ink may be achieved by altering the relative amount(s) of some or all of the formulation components. Such adjustments may render the composition usable in applications other than newspaper printing. 
     Relatively small variations in the amount of triethanolamine contained in the ink composition of Example I have been found to cause substantial corresponding variations in the rheological properties of the ink. For example, Table A contains shear rate versus viscosity values for ink compositions containing all the ingredients set forth in Example I, but wherein the concentration of TEA has been varied from 0% to 5% by weight. The viscosity values set forth in Table A were measured at 37° C. using a Brookfield viscosimeter fitted with a CP-52 spindle. 
     
                       TABLE A                                                     
______________________________________                                    
                                  Brookfield                              
      Shear Rate Shear Stress     Viscosity                               
RPM   (sec.sup.-1)                                                        
                 (dynes/cm.sup.2) (CPS)                                   
______________________________________                                    
Sample A (0.0% TEA)                                                       
0.5    1          0.71841         71.841                                  
1.0    2          0.99472         49.736                                  
2.5    5         1.4644           29.289                                  
5.0   10         1.7960           17.960                                  
10    20         2.3763           11.881                                  
20    40         3.3986            8.4966                                 
50    100        5.2499            5.2499                                 
100   200        7.4604            3.7302                                 
Sample B (0.5% TEA)                                                       
0.5    1          0.69078         69.078                                  
1.0    2          0.93946         46.973                                  
2.5    5         1.5750           31.499                                  
5.0   10         1.8789           18.789                                  
10    20         2.5697           12.848                                  
20    40         3.6473            9.1183                                 
50    100        5.8025            5.8025                                 
100   200        8.2064            4.1032                                 
Sample C (1.0% TEA)                                                       
0.5    1         1.4368           143.68                                  
1.0    2         1.9065           95.327                                  
2.5    5         2.9842           59.683                                  
5.0   10         3.5920           35.920                                  
10    20         4.4486           22.243                                  
20    40         5.3881           13.470                                  
50    100        8.3170            8.3170                                 
100   200        11.218            5.6091                                 
Sample D (1.5% TEA)                                                       
0.5    1         1.6302           163.02                                  
1.0    2         1.8513           92.564                                  
2.5    5         2.3763           47.525                                  
5.0   10         2.7907           27.907                                  
10    20         3.2328           16.164                                  
20    40         4.2828           10.707                                  
50    100        7.3222            7.3222                                 
100   200        10.223            5.1117                                 
Sample E (2.0% TEA)                                                       
0.5    1         1.2158           121.58                                  
1.0    2         1.3539           67.696                                  
2.5    5         1.5197           30.394                                  
5.0   10         1.575            15.750                                  
10    20         1.9342            9.6709                                 
20    40         2.6802            6.7005                                 
50    100        4.1999            4.1994                                 
100   200        5.8025            2.9013                                 
______________________________________                                    
 
    
     The foregoing tabular data evidences and illustrate the highly desirable thixotropic properties obtained when the amount of TEA contained in the ink formulation of Example I is varied between 0.5 and 2.0% by weight. Based on these data, thixotropic properties suitable for most newspaper printing applications are obtained when TEA is included in the formulation at approximately 0.7% by weight. 
     EXAMPLE II 
     A red ink formulation in accordance with the invention comprises: 
     
         ______________________________________                                    
RED INK FORMULATION                                                       
                                 % By                                     
Component      Source            Weight                                   
______________________________________                                    
A:  Heatset Varnish                                                       
                   HSLM Camel; The Ink                                    
                                     35%                                  
    (IC34)         Co., Sacramento, CA                                    
B:  Gelled Ink Oil BOSO; The Ink Co.,                                     
                                     5%                                   
    (IC31)         Sacramento, CA                                         
C:  Rubine Ink Base                                                       
                   DBE Rubine; The Ink Co.,                               
                                     20%                                  
                   Tampa, Florida                                         
D:  Red Pigment Compo-                                                    
                   Red Lake C; Magruder                                   
                                     2%                                   
    sition         Color Co., Elizabeth, NJ                               
E:  Naphthenic Ink Oil                                                    
                   High Print L1200; Ergon                                
                                     32%                                  
    (1-1200 Oil)   Refining Co., Vicksburg,                               
                   Miss.                                                  
F:  Triethanolamine                                                       
                   99%, Union Carbide                                     
                                     2%                                   
G.  Petroluem Hydro-                                                      
                   Magiesol 52 Oil; Magie                                 
                                     4%                                   
    Carbon Oil     Brothers Oil Co.,                                      
    (Hydro-Treated Franklyn Park, Ill.                                    
    52-A Oil)                                                             
______________________________________                                    
 
    
     The red ink formulation set forth in Example II is prepared by initially combining 35% heatset varnish (IC34) (component A), 5% gelled ink oil (component B), 20% rubine ink base (component C), and 2% red pigment composition (component D) in a single vessel, and mixing at room temperature until a substantially homogenous and even consistency is achieved. Thereafter, a first aliquot or portion (18%) of the naphthenic ink oil (component E) is added to the vessel and the vessel contents are mixed until uniformity and homogeneity have been achieved. Thereafter, the remainder (14%) of the naphthinic ink oil (component E), 2% triethanolamine (compound F), and 4% 52A oil (compound G) are added under continued mixing. The TEA may be added at room temperature. It is not necessary to heat the composition in order to obtain the desired thixotropic effects of TEA. However, it will be appreciated that the other components of the formulations are generally blended at elevated manufacturing temperatures of approximately 200° C. Thus, to facilitate processing, the TEA may be added while the formulation is at such elevated temperature. 
     EXAMPLE III 
     A primarily resin-based ink formulation in accordance with the invention comprises: 
     
         ______________________________________                                    
                                % By                                      
Component     Source            Weight                                    
______________________________________                                    
A:  Heatset Varnish                                                       
                  HSLM Camel; The Ink                                     
                                    35.5%                                 
    (IC34)        Co., Sacramento, CA                                     
B:  Rubine Ink Base                                                       
                  DBE Rubine; The Ink Co.,                                
                                    39.0%                                 
                  Tampa, FL                                               
C:  Printing Ink Wax                                                      
                  L-386 Wax, Dyall   7.0%                                 
    Compound      Products, Franklin                                      
                  Park, IL                                                
D:  Petroleum Based                                                       
                  Magiesol 52 Oil;  15.5%                                 
    Ink Solvent   Magie Brothers                                          
    (hydro-treated                                                        
                  Oil Co., Franklyn                                       
    52A Oil)      Park, IL                                                
E:  Triethanolamine                                                       
                  Union Carbide Corp.,                                    
                                     2.0%                                 
    (99%)         Princeton, NJ                                           
F:  Polymarized   H-2 Out            0.5%                                 
    Castor Oil    CPS; Buffalo, NY                                        
______________________________________                                    
 
    
     The red ink formulation of Example III is prepared by initially combining the Heatset Varnish (component A) and the Rubine Ink Base (component B) and mixing until smooth. Thereafter, the remaining ingredients (components C through G) are added slowly, under mixing. The TEA may be added at room temperature. It is not necessary to heat the composition in order to obtain the desired thixotropic effects of TEA. However, it will be appreciated that the other components of the formulations are generally blended at elevated manufacturing temperatures of approximately 200° C. Thus, to facilitate processing, the TEA may be added while the formulation is at such elevated temperature. 
     EXAMPLE IV 
     A primarily oil-based ink composition of the present invention comprises: 
     
         ______________________________________                                    
Component     Source         % By Weight                                  
______________________________________                                    
A:  Naphthenic Ink Oil                                                    
                  Hyprint L-1200;                                         
                                 73.0%                                    
    (1-1200 Oil)  Ergon Refining,                                         
                  Vicksburg, Miss.                                        
B:  Oil-Based Carbon                                                      
                  ELFEX 115;     20.21%                                   
    Black         Cabot Corp.,                                            
                  Cabot, LA                                               
C:  Petroleum-Process                                                     
                  Telura 797; Exxon                                       
                                 6.1%                                     
    Oil           Chemical Corp.,                                         
                  Houston, Texas                                          
D:  Triethanolamine                                                       
                  Union Carbide Corp.,                                    
                                 0.55%                                    
    (99%)         Princeton, NJ                                           
______________________________________                                    
 
    
     The black ink formulation of Example IV is prepared by initially combining the naphthenic ink oil (component A), the oil-based carbon black (component B), and the petroleum-process oil (component C) and blending such combined components until a homogenous mixture is attained. Thereafter, the triethanolamine (TEA) (component D) is added under mixing. The TEA may be added at room temperature. It is not necessary to heat the composition in order to obtain the desired thixotropic effects of TEA. However, it will be appreciated that the other components of the formulations are generally blended at elevated manufacturing temperatures of approximately 200° C. Thus, to facilitate processing, the TEA may be added while the formulation is at such elevated temperature. 
     Having described the present invention with specific reference to the foregoing examples, it will be obvious to those skilled in the art that various additions, deletions, and modifications may be made to the exemplary formulations without departing from the spirit and scope of the invention. Accordingly, such additions, deletions, and modifications are not to be regarded as departures from the spirit and scope of the present invention, but rather are intended to be included within the scope of the following claims and the equivalents thereof.